1. Field of the Invention
This invention relates to a communication apparatus and method, and more particularly to a communication apparatus and method which are suitable for communicating various kinds of information.
2. Description of the Related Art
In the case of using a conventional analog telephone circuit as a communication apparatus, the telephone itself can transmit only voice data, and all types of data can be transmitted only at a low speed.
Recently, however, as a result of progress in communication technology, semiconductor technology and optical technology, digital networks have been provided, and it has become possible to transmit large quantities of data at high speed.
Such digital transmission has advantageous features in that, for example, the same level of data quality can be maintained without degradation during data transmission. Also, a particular transmission channel corresponding to the characteristics of the kind of transmitted data is not required, and therefore all media can be dealt with. Hence, it has become possible to perform transmission between complex media terminals and, as a result, multimedia communication apparatuses have appeared in which a telephone can simultaneously transmit images as well as voice data.
International standardization by the ITU-T and the like has intended to ensure that mutual communication can be performed between terminals which deal with voice data and image data, and service provisions, protocol provisions, and provisions for the configuration of multimedia multiplexed frames for AV (audiovisual) services, such as video telephones, video conferences, and the like using a digital network, have been announced as H. 320, H. 242, H. 221, and the like recommended by the ITU-T.
In H. 221, the frame configuration, exchange of terminal capabilities, and code allocation of an FAS (frame alignment signal) and a BAS (bit allocation signal) in a communication mode in AV series for 64 Kbits to 1920 Kbits are defined.
In H. 242, protocols for the exchange of capabilities between AV terminals using a BAS, the switching of the communication mode, and the like are defined. In H. 320, system aspects for all AV services are defined.
In the above-described recommendations, methods are provided for performing the communication of multimedia, comprising images, voice, data, and the like between terminals according to procedures, such as a sequence of in-channel exchanges of terminal capabilities using a BAS, a mode-switching sequence by assigning a communication mode and the like after setting of an end-to-end physical connection and in-channel establishment of synchronization using a FAS.
However, methods for changing the capabilities of a terminal in accordance with a new situation, and methods of selecting a communication mode within the range of exchanged capabilities, are not provided.
In multimedia communication, the information transfer speed for voice information is determined by assigning a voice-encoding method, and the transfer speed for data information is determined by assigning the value of the transfer speed when data information is transferred. The transfer speed for image information is obtained by subtracting the transfer speed for voice information and the transfer speed for data information from the set information transfer speed of the entire communication channel.
However, such conventional communication apparatus have certain problems.
For example, a first user at one terminal can send document information in a first communication to another terminal, and the first user at the one terminal can talk about the document with a second user at another terminal in a second communication. In this situation, the second user will have to be careful to keep any copy of the document.
If the second user loses the document, the second user has to have the first user send the document again.
Therefore the conventional apparatus is not always easy to use.
The above example refers to document information and voice data transmitted while talking, but the above problem is not limited to document and voice data. For other media, e.g. image data, motion image data and text data, similar problems will occur.
Besides, a multimedia communication apparatus has many functions, e.g. facsimile transmission, voice data transmission, image data transmission, and so the apparatus may not send information that describes all the functions of the apparatus.
Therefore, each terminal has to request the communication partner's terminal to send the information, and it can take a relatively long time to send the information.